Conventional geothermal heat recovery systems are employed to extract thermal energy from subterranean heated formations through heat exchange with rock using water as the heat exchange medium. In the same way, fluids from the high temperature side of any thermal process can be cooled through heat exchange with cooling water from cool subterranean formations.
Heat exchangers are used in industrial processes to cool heated process fluids before discharging the fluids to the environment. For instance, heat exchangers are used in thermal cycle power plants to decrease the discharge temperature of working fluid exiting a turbine that drives an electrical generator. The efficiency of the thermal cycle increases as the discharge temperature of the working fluid decreases. Water is commonly used in wet cooling cycles because water has a high heat capacity. However, water is not always available and is often allocated for other uses including irrigation, drinking and/or other industrial uses. Water is particularly scarce for cooling uses in projects located in arid areas.
Current wet cooling cycles used in thermal cycle power plants include once through cooling cycles and evaporative cooling cycles. Once-through cooling involves circulating water from a water body or an aquifer through the cooling cycle and then disposing of the heated water into the same or other water body. Evaporative cooling involves circulating cooling water between the cooling cycle and an evaporative cooling tower where the water is cooled.
In once-through cooling cycles, water is not usually consumed and water temperature generally increases less than 10° C. However, large volumes of water are necessary for cooling. Once through cooling cycles require between four and twelve gallons of cool water per minute per kilowatt electricity generated. Heated water is returned to surface water bodies which can adversely impact plant and animal life that is sensitive to minor variations in water temperature.
Evaporative cooling cycles result in approximately 70 to 80 percent water loss on an annual basis, which is equivalent to one to three gallons per minute per kilowatt electricity generated. Recirculation of cooling water through the evaporative cooling tower increases the concentration of dissolved solids and minerals that are common in water and brine produced from geothermal wells. Scale and corrosion inhibiters and other chemicals are required to prevent scale, corrosion and growth of organisms such as algae in the oxygen rich cooling cycle. This water, if disposed of to surface water bodies, can cause environmental damage.
Current cooling systems and methods that are used in industrial processes including, but not limited to, flash steam power plants, binary power plants and solar thermal power plants are inefficient, require large volumes of water and are harmful to the environment.